Dynamic joint motion analysis technique

ABSTRACT

A three-plane goniometer or angle measuring apparatus includes three small potentiometers which are closely spaced together to measure rotation of the knee about three different axes. The unit is primarily mounted on a cuff on the outside of the thigh. The mounting assembly for the three plane goniometer includes a curved yoke where the ends of the yoke curve from the front to the rear, with the goniometer unit being held between the ends of the rearwardly extending arms of the yoke, so that accurate measurement may be maintained in all three planes even while the knee is bent to its extreme flexed position. Extending downwardly from the goniometer is a square rod which slidably engages a square hole in a nylon ball mounted in a two-axis gimbal, which is secured to a cuff strapped to the calf of the leg. Injuries may be diagnosed or characterized by comparing the pattern for one leg before injury with the pattern for that leg after injury or by comparing the pattern for one (healthy) leg with that for the other (injured) leg. The goniometer is mounted so that it may be readily reversed and used for both the right and left legs. Associated processing circuitry includes corresponding reversing circuits for conforming the plots for the right and left leg, and also includes special face marking circuitry. Comparative tests may be made for different types of footwear and athletic playing surfaces, and the torque which is produced may be compared to determine the preferred foot gear or playing surface.

FIELD OF THE INVENTION

This invention relates to dynamic joint measuring techniques, and moreparticularly to arrangements for measuring and analyzing dynamic motionof the knee and other joints in three planes.

BACKGROUND OF THE INVENTION

It has previously been proposed to measure knee motion in all threeplanes, and a typical article disclosing such measurement is "AnElectrogoniometric Study of Knee Motion in Normal Gait" by Donald B.Kettelkamp, M.D., et al., the Journal of Bone and Joint Surgery, Volume52-A, No. 4, June 1970, pages 775 to 790.

In general, what the prior analyses show is that the human knee is arelatively complicated joint, and its motion is not limited tohinge-type action around a single transverse axis as might initially beexpected of the knee joint. This front-to-back motion, which of courseis the principal and major motion of the knee, is known asflexion-extension. Full extension of the knee is when the leg isstretched out and the knee joint locked; and full flexion of the kneeoccurs when the leg is bent so that the calf is firmly against thethigh. Studies of the knee show that in the course of normal walking,for example, the knee goes through two flexion-extension cycles duringeach complete walking step, with maximum extension occuring during theswing phase, and an additional extension occurring during the time whenthe foot is engaging the ground. In addition to the flexion-extensionmotion, the knee also bends toward and away from the centerline of thebody. This inward or outward motion is known variously asabduction/adduction, or varus/valgus motion, with "abduction" and"varus" referring to outward movement of the knee, and "adduction" and "valgus" referring to inward movement of the knee. In the presentspecification, we will use the designation varus/valgus but some of theprior articles use the comparable terms abduction/adduction. In additionto the two types of rotation mentioned above, the knee also may rotateabout the long axis of the leg. This rotation is referred to asinternal/external rotation. In summary therefore, the three types ofmotion of the knee to which reference will be made in the presentspecification are (1) flexion/extension, (2) varus/valgus, referring tothe inward or outward bending of the knee, and (3) internal/externalrotation.

The apparatus which has been employed up to the present time has beenrelatively cumbersome and massive, and the measurements which have beenobtained have been similarly somewhat qualitative and inconsistent.

Accordingly, objects of the present invention include the provision of alighter weight three-axis goniometer which is capable of measurement ofathletes performing rapid and extreme physical movements, and one whichwill provide accurate and reliable information under such arduousconditions.

Another object of the present invention in to provide for the diagnosisof knee injuries by comparing a pattern produced by one leg beforeinjury with the pattern produced by that leg after injury or bycomparing the pattern produced by one (healthy) leg with that producedby the other (injured) leg.

Still another object of the present invention is to determine the torquewhich is produced under successive different controlled test conditions,for the purpose of testing athletic equipment or environments, such asfoot gear and playing surface qualitites, by way of specific examples.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention a lightweightthree-axis goniometer is provided with arrangements for mounting it onthe outside of the thigh of a user, and the goniometer is supported fromthe thigh by a yoke, which has its ends on which the goniometer ispivotally mounted extending to the rear, to preclude mechanicalinterference in the course of the measurement of the movement of theknee in all three planes, despite concurrent extreme angular movementsof the knee. In addition, arrangements may be provided for reversing themounting of the goniometer on the mounting support, so that the sameunit may be first used on one leg and then on the other. In thisconnection, it may be noted that, with a normal healthy person, thecharacteristic angular movements of the knee in all three planes arevery nearly the same for the left and right knees. Accordingly, when aperson has one leg injured, by using the healthy leg as a control, andthen measuring the injured knee, considerable diagnostic information maybe obtained. Similar information may be obtained by measuring the sameknee before and after injury.

In accordance with another aspect of the invention, the goniometer maybe employed to indicate the torque applied to the leg by differentathletic equipment conditions. For example, when a football player isplaying on an artificial surface, the effect of using different types offootball shoes with different cleat configurations or materials, forexample, on an artificial turf can be measured in the course ofnegotiating a standardized course in a predetermined period of time. Theresultant comparative tests indicating the extreme angular deviationsfor two sets of conditions may be compared, and equipment or playingsurface selections may be made based on such comparisons. One directapplication of this type of testing is the selection of shoes forathletes that will minimize stress to the knee while still providingadequate traction, such selection possibly varying as playing surfaceconditions vary. Another direct application of this type of testing isto fit individuals with shoes based upon their particular anatomy suchthat stress to the knee will be minimized while walking or running.Still another direct application of this type of testing is theselection of playing surfaces which consistently minimize stress to theknee.

In the data processing circuitry employed in the processing of signalsfrom the goniometer, switches may be provided for the reversing of thevarus/valgus and the internal/external rotation signals, as thegoniometer is switched from the left leg to the right leg, or viceversa, so that the plots for the two legs will have the sameconfiguration, and may be more readily compared. In addition, theelectronic circuitry may include a trace identification patternassociated with one or more of the three output signals from thegoniometer, and if desired, these signals may be interrupted as theassociated signal shifts from positive to negative or vice versa.

Other mechanical features of the goniometer assembly include (1) the useof high strength, lightweight plastic such as Delrin for the unit, (2)locating the potentiometers very close together, so that thepotentiometer subassembly is less in extent than two inches, forexample, (3) the use of mounting assemblies for securing the goniometerunit to the upper leg mount which lock positively in either of twoorientations which are 180 degrees displaced from one another forreversing purposes, and (4) the use of a sliding rod which extendsthrough an element such as a nylon sphere, mounted in a two axis gimbalon the lower leg, all for the purpose of measuring internal/externalrotation.

Other objects, features, and advantages of the present invention willbecome apparent from a consideration of the following detaileddescription and from the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a three plane goniometer and mounting assemblymounted on the leg of a person being tested;

FIG. 2 is a front view of the arrangement of FIG. 1;

FIGS. 3 and 4 are mutually orthogonal views of the goniometer and thelower mounting assembly secured to the upper leg, and relating to theunit shown in FIGS. 1 and 2.

FIG. 5 shows the unit partially disassembled to permit reversing for useon the other leg;

FIG. 6 shows an alternative lighter weight embodiment in which only asingle mounting tube is employed instead of the three tubes shown in theunit of FIGS. 1 through 5;

FIG. 6A is an enlarged view of one portion of the unit of FIG. 6;

FIG. 7 is a showing of a unit, including a gimbal subassembly, forsecuring to the lower leg;

FIG. 7A is an enlarged view of one portion of the unit of FIG. 7;

FIG. 8 is a plot comparing normal knee motion with knee motion in whichone of the ligaments, the anterior cruciate ligament, is weak, or hasbeen damaged;

FIG. 9 is a plot of torque versus internal/external knee rotation;

FIGS. 10A and 10B are two parts of the circuit diagram of the circuitfor amplifying and recording the signals received from the goniometerunits described hereinabove; and

FIGS. 11A and 11B show the classic differences between a normal knee anda knee in which a lateral miniscus or other lateral compartment injuryis present.

DETAILED DESCRIPTION

Referring more particularly to the drawings, FIG. 1 is a side view ofthe leg of a man with a three axis goniometer assembly 12 mounted nearthe knee. The goniometer assembly 12 is mounted from three tubes 14, 16and 18 which slide into the three additional mounting tubes 20, 22 and24. The tubes 20, 22 and 24 are mounted in two brackets 26 and 28, whichare secured to a mounting pad 30, which is in turn mounted on the outerside of the man's thigh by adjustable straps 32 and 34 provided withVelcro or other suitable arrangements for securing the straps around thewearer's upper leg.

As indicated in FIGS. 3 and 4, the lower mounting unit 28 is adjustableto permit the goniometer assembly 12 to be moved closer or farther awayfrom the knee, all depending on the musculature and the generalconfiguration of the thigh relative to the knee, with the goal being tolocate the goniometer assembly 12 as close as possible to the knee. Thetubes 14, 16 and 18 are slidable within the tubes 20, 22 and 24, and areheld in their desired position so that the goniometer assembly 12 isproperly located relative to the knee by the knurled adjustment screws36.

The central tube 16 is longer than the two outer tubes 14 and 18, sothat, as shown in FIG. 5, when it is desired to reverse the position ofthe goniometer assembly 12 to mount it on the left leg, the knurledscrews only have to be loosened, and tube 14 is first slid out of tube20 and then, following rotation, it is slid back into tube 24 and tube18 slid back into tube 20. Incidentally, the leads from thepotentiometers 42, 44 and 46 which are included in the goniometerassembly 12 extend up through the central tubes 16 and 22.

Inward and outward adjustment of the goniometer assembly 12, toward andaway from the knee, is accomplished by adjustments involving the pairsof knurled knobs 48 and 50 (see FIG. 4). A screw secured to one of thetwo knobs 48, is threaded into the other of the knobs 48, whereby theslanted and movable internal beam 52 may be shifted in its anglerelative to the pad 30 as the shanks of the screws associated withknurled knobs 48 and 50 move in the slots 54 and 56. The lower tubesupporting element 58 is pivotally secured to the plastic member 52 bypin 60, and is otherwise held in its proper alignment by the orientationof the tubes 20, 22 and 24 which are also pivotally mounted at theirupper ends on the plastic element 26 (see FIGS. 1 and 2).

Extending downwardly from the potentiometer 46 is a metal rod 64 whichhas a lower end 66 which is of square or other non-circularconfiguration. The square rod 66 passes through and is slidable within anylon sphere 68, which has a central rectangular opening and which ismounted in a two-axis gimbal arrangement 70 shown in FIGS. 7 and 7A, andwhich in turn is mounted on a cuff 72 secured to the lower leg bysuitable straps 74 which are somewhat elastic and which are adjustablein the same manner as the straps 32 and 34 employed to secure the cuff30 to the thigh.

The cuffs include a sheet aluminum alloy, which is approximately 0.032inch thick. The sheet aluminum is covered with vinyl material on itsexterior surface, and the cuffs are provided with a one-quarter inchthick foam rubber layer on their interior surfaces.

As best shown in FIGS. 3 and 4, the goniometer assembly 12 includes twopotentiometer housings 40 and 41 which house the three precisionpotentiometers 42, 44 and 46 (potentiometers 42 and 44 in housing 40 andpotentiometer 46 in housing 41). The potentiometer 42 is operated by apin 76 which extends outwardly from the potentiometer 42 and is securedto the end of the yoke having the two rearwardly extending arms 78 and80. The potentiometer 42 measures flexion/extension, the normal majorpivotal motion of the knee, and is capable of measuring up to 145degrees. The cutaway configuration of the support member 82 with itssubstantial opening 84 provides for the varus/valgus motion as measuredby potentiometer 44 as well as for internal/external rotation asmeasured by potentiometer 46, without mechanical interference, despite afull range of movement of the three potentiometers about the pin 76.

As discussed earlier, FIG. 5 shows the method of rotation of thegoniometer assembly 12 relative to the mounting pad 30 and theassociated bracket 28. Specifically, the knurled knobs 36 are loosened,the three tubes 14, 16 and 18 are slid downward until only the centraltube 16 which carries the electrical conductors is in engagement, andthe unit is rotated by 180 degrees so that tube 14 engages tube 24, andtube 18 engages tube 20 and the unit is then reassembled for the use onthe left leg. Again, with the new orientation of the unit, and with thecuff 30 mounted on the left leg, the ends of the yoke members 78 and 80will again be directed to the rear, and the unit will accommodate thefull range of flexion/extension motion of the left leg. It may be notedin passing, that in the absence of arrangements for reversing the unitas it is shifted from the left leg to the right leg or vice versa, thepotentiometer 42 for measuring flexion-extension would have differentangular ranges for the right and left leg, and the curved yoke includinglegs 78,80 would not provide clearances for the extreme rotation aboutseveral axes simultaneously for both the right and the left leg.Accordingly, without reversibility, some decrease in sensitivity, and/ormechanical interference with extreme motion, is to be expected.Alternatively, a much more bulky and heavy unit would have to beemployed.

FIGS. 6 and 6A show an alternative and somewhat lighter embodiment ofthe invention in which only one tube 86 slidable within the mountingbracket 94 and the lower pivoted plastic member 98 is used. The threeaxis goniometer 90 is similar in configuration to the unit 12 asemployed in the arrangements of FIGS. 1 through 5, but is slightlysmaller and lighter in weight. Again, it includes a yoke with rearwardlydirected arms for increased mechanical clearance, and threepotentiometers. The unit of FIG. 6 is very similar to that of FIGS. 1through 5 and employs a cuff 92 with associated straps, and a similarupper mounting bracket 94 and a lower mounting bracket 96. The lowermounting bracket 96 is provided with similar arrangements for adjustingthe height of the lower pivoted plastic member 98 which correspondsgenerally to the pivoted member 58 as shown in FIG. 4. The front bracketmember 98 is provided with a knurled clamping nut 100 to hold the tube86 in one of two orientations, which are 180 degrees displaced from oneanother. These two orientations are accomplished through the use of arectangular plastic block 102 which is secured to the tube 86 and whichis held in its proper orientation by the upper and lower protruding lips104 extending downwardly from the block 98. With this arrangement, andwith the block 102 being slightly wider than it is high, there are onlytwo possible orientations with block 102 in engagement with member 98,one being for use on the right leg and the other for use on the leftleg.

FIGS. 7 and 7A show the arrangement whereby internal/external rotationof the knee as measured at the lower leg rotates the shaft 64 and inturn rotates the potentiometer 46 or the corresponding potentiometer ofthe single tube arrangement of FIG. 6. As mentioned above, the lower end66 of the shaft 64 has a non-circular or square configuration, and isjournalled in the nylon ball 68 in order to permit the rod 64 to freelyslide up and down relative to the element 68. Further, in order topermit changes in angle of the rod 64 relative to the cuff 72, atwo-axis gimbal is provided which includes the U-shaped frame 112 whichis secured to the cuff 72. Mounted in the U-shaped frame 112 is thegimbal ring 114, and it in turn mounts the ball 68 about an axis whichis perpendicular to the base 112. With this arrangement, changes inalignment of the shaft 64 relative to the cuff 72 are readily permitted,but actual rotation of the lower portion of the leg is fully transmittedto the shaft 64 and result in changes in the output from potentiometer46.

The plots of FIG. 8 represent the culmination of the use of the units asdescribed hereinabove, together with the processing and recordingcircuitry to be discussed below. In FIG. 8, an injured knee is comparedwith a normal knee by switching the unit as described hereinabove fromone leg to the other. Plots from the "control" or normal knee are shownin solid lines, while output plots from the injured knee are shown bydashed lines. In FIG. 8 the top graph represents flexion/extension, themiddle graph represents varus/valgus movement, and the lowermost graphrefers to internal/external rotation. The first portion, proceeding fromleft to right represents a normal walking pattern, the second portionbetween lines 122 and 124 represents a cross-over turn, the next sectionbetween lines 124 and 126 is again normal walking while the spacebetween lines 126 and 128 represents a sidestep, and this is followedagain by normal walking.

In reviewing the normal knee plots as shown in the solid lines, it isnoted that there are two maxima in leg flexion or bending which occurduring each cycle of walking from one heel strike to the next heelstrike, for example. One of these maxima occurs while the leg isswinging and the other smaller maxima or peak occurs while the foot isin engagement with the ground. A similar pattern, but with less angularextent is present with the varus/valgus characteristic and also with theinternal/external rotation characteristic. Further, while the overallmagnitude of the characteristics vary from person to person, thepatterns are normally quite similar. In addition, and as mentionedabove, for any particular individual, the left leg and the right legnormally produce patterns which have maxima and minima which are verynearly the same, and with the entire patterns being substantially thesame, when there is no injury present.

If there were no injury present in the person being examined in FIG. 8,the solid line plot would be very nearly identical with the dashed lineplot, or vice versa. However, in FIG. 8, there are in fact a number ofsignificant departures of the injured knee characteristic as shown indashed lines, as compared with the normal knee. These are emphasized bythe circles 132, 134, 136 and 138. As indicated on the chart, the circle132 indicates guarded internal rotation while walking; and all of thenext three anomalies are involved in the cross-over turn which isaccomplished between lines 122 and 124. Specifically, the encircled area134 in the internal/external rotation characteristic shows externalrotation anticipating a cross-over; the encircled area 136 shows avariation in the valgus thrust, and the encircled area 138 indicatesinhibited extension during cross-over.

As may be appreciated from the foregoing discussion, the knee is by nomeans a simple hinge-type joint, but is relatively complex. Morespecifically, the lower end of the femur, or heavy upper leg bone, isprovided with two rounded protruberances, and these seat in the upperend of the tibia, which is the larger, lower leg bone. Two ligamentsextend at angles across the knee joint, with these two crossingligaments being referred to as the anterior cruciate and posteriorcruciate ligaments, the anterior cruciate extending across from theupper outer side of the knee to the lower inner side of the knee infront of the posterior cruciate which extends from the upper inner sideof the knee across behind the anterior cruciate toward the lower outsideof the knee.

The pattern of departure from nomality indicated by FIG. 8 represents ananterior cruciate ligament insufficiency. As developed below, otherinjuries to the knee produce characteristic anomalies in the pattern ofnormal and injured knee movement when standardized procedures areundertaken of the type described hereinabove in connection with FIG. 8.These characteristic patterns can be a useful diagnostic tool toindicate the type of injury, or the compartment in which the injury isprobably located. Incidentally, in many cases, following diagnosis bynormal techniques, the methods of analysis as described herein hasresulted in an improved, changed or more complete diagnosis which wasuseful in directing the corrective surgery or other medical techniques.

Consideration will now be given to torque applied to the knee.Initially, it must be clearly understood that a three-plane orthree-axis goniometer does not measure torque. However, because of thetorque versus angular rotation characteristic of the normal knee, themagnitude of the angle of internal/external rotation is a good indicatorof changes in knee torque, under different conditions.

FIG. 9 is a plot of the average value of torque required to produceangular rotation of the tibia for seven normal knees. While the absolutevalue of the individual points of this plot may differ with a differentgroup of knees, the shape and slopes will be similar for most normalknees.

In the course of studying different types of athletic shoes, an athleteinitially wearing shoe "A" performed a specific set of manuevers whichis known to rotationally stress the knee a predetermined number of timessuch as 10 times. The results of these tests showed that the averagevalue of maximum internal tibial rotation was 20 degrees, and referenceto FIG. 9 shows that 20 degrees of internal rotation is produced by atorque of approximately 3 Nm (Newton-Meters) on the joint. Subsequently,using shoe "B", the athlete repeated the same maneuvers on the samesurface for the same number of times. For shoe "B" the average value ofmaximum internal rotation was 25 degrees, and reference to FIG. 9reveals that approximately 7 Nm of torque is required to produce 25degrees of tibial rotation. Accordingly, shoe "B" apparently transmits21/2 times the torque to the knee as shoe "A" for the same activity. Andserious consideration must be given as to whether shoe "B" may safely beused in view of the greatly increased torque which is produced. Ofcourse, torque is only one factor to be considered, and the degree ofcontrol achieved by the athlete with the two shoes must obviously beconsidered and perhaps a suitable compromise shoe configurationselected.

It is also noted that the qualities of various playing surfaces may alsobe tested by repetitive activity on the different surfaces using asingle pair of shoes on both surfaces, and a standardized series ofmaneuvers. Such tests could be useful in the design or selection ofsuitable natural substances or artificial "carpets" to be employed ascoverings for athletic fields. It is also noted in passing that tiringof the athlete may be a factor; accordingly, the athlete should eitherrest between successive series under different conditions, or alternatetests, first using one set of conditions, then the other, and continuingsuccessive alternations.

Still another specific example of how the goniometer readings may beused is the fitting of shoes to an individual such that stresses to theknee will be minimized. Because of differences in the physical make-upof individuals, some shoes create considerable stresses to the knee,while others will dampen such stresses. The inward or outward slant of ashoe sole has such effects depending on how an individual's footnormally contacts the ground. By having a person negotiate standardmaneuvers wearing different shoes and comparing goniometer readings, theshoes that are best for that person from a knee stress standpoint can befound.

Still another specific example of how the goniometer readings may beused is the selection of shoes for athletes that will minimize kneestresses while providing adequate traction on varying playing surfaces.Most teams, such as football, soccer, baseball, etc., today play on avariety of surfaces depending on location and weather. One such surfacefor a given athlete with a given pair of shoes might create kneestresses of a relatively small magnitude, while another surface with thesame athlete and shoes might create knee stresses of a dangerously highmagnitude. By having the athlete perform standard maneuvers withdifferent shoes on any given field and comparing goniometer readings,the shoes from that lot that are best in minimizing knee stresses whileproviding adequate traction, can be selected.

FIGS. 10A and 10B together form a circuit for processing the signalsfrom the three axis goniometers described hereinabove. Moreparticularly, the leads from the three potentiometers are connectedthrough one of the tubes, and are brought through the tubes onto thewearer's body. In the case of routine walking tests, such as thosedescribed in connection with FIG. 8, long leads may be employed toconnect to the connector block 142 as shown in FIG. 10A. Alternatively,in the event that more freedom of activity to conduct wider-rangingtests is required, simple telemetry arrangements could be employed toroute the signals from the person wearing the goniometer assembly to theprocessing and recording equipment of FIGS. 10A and 10B. In all events,signals from the three axis goniometer are routed to the connector 142and from this connector the flexion/extension signals are routed tochannel 144, the varus/valgus signals are routed to channel 146, and theinternal/external rotation signals are routed to channel 148.

There are two instrumentation amplifiers A and B associated with each ofthe channels 144, 146, and 148. The reason for these two instrumentationamplifiers involves the different resistor settings required toaccommodate the different impedances provided by the three axisgoniometer as shown in FIGS. 1 through 5, and that shown in FIG. 6.Accordingly, when a switch is made from one of the goniometers to theother, the switch 150 is actuated to select signals from either the "A"or the "B" set of instrumentation amplifiers. The sensitivitycontrolling potentiometers 152, 154 and 156 control the sensitivity forflexion/extension, varus/valgus and internal/external rotation, as themaximum values for these various parameters may vary from patient topatient. Immediately after the sensitivity controlling potentiometers152, 154 and 156, are found the voltage follower circuits 158, 160 and162, respectively. Associated with the varus/valgus and theinternal/external rotation channels are the polarity reversing circuits164 and 166, respectively. The switch 168 serves to reverse the polarityand it is actuated as the three axis goniometers are switched from oneleg to the other of a patient, thereby facilitating comparison of plotsmade by the left and right legs.

The switch 170 is the galvanometer on-off switch. The circuitryassociated with chip 172 is a warning signal which energizes the warninglamp 174 when the galvanometers are turned off, to avoid an attemptedtest cycle with a patient proceeding through the specified maneuverswhen the galvanometers are turned off. A recorder unit is generallyindicated by the dashed line block 176. Within the block 176 are shown aseries of three galvanometers 178, 180 and 182 associated respectivelywith the three channels corresponding to the three outputs from thegoniometers. The two additional galvanometers 184 and 186 provide markersignals for the varus/valgus and internal/external rotation channels, asshown in FIGS. 11A and 11B to be described below. More specifically, alow frequency signal in the order of 10 to 30 hertz is provided by anysuitable oscillator 188. The field effect transistors 190 and 192selectively block the oscillator signal from the galvanometers 184 and186 when the corresponding signals pass through a predetermined level.This serves to uniquely identify the particular signals associated withthat channel and avoid their confusion of traces associated withadjacent channels, despite some occasional overlap. This will be shownin greater detail in connection with FIGS. 11A and 11B. The inputcircuits to the field effect transistors 190 and 192 are comparisoncircuits which establish the levels at which the FET's will block thesignals from oscillator 188.

Now, referring to FIGS. 11A and 11B, the upper trace in each caserepresents flexion/extension; the central trace represents varus/valgus;and the lower trace represents internal/external rotation, in accordancewith the normal practice in displaying these features. In FIG. 11A, thesignal from the oscillator 188 appears at 196 and 198, and isinterrupted between these two data plots, indicating that thevarus/valgus signal exceeded the predetermined level represented by thelowermost extreme of the plots 196 and 198. Similarly, the markerpattern designated by the reference numerals 200 and 202 associated withthe flexion/extension characteristic in FIG. 11A, is interrupted whenthe characteristic exceeds a predetermined level.

The plots of FIG. 11A are the graphs from a healthy right leg. However,the plots of FIG. 11B represents an injured left leg, which includes alateral meniscus tear. In this case, the internal/external rotation isrelatively normal, but there are anomalies in the flexion/extension andin the varus/valgus characteristics. More specifically, theflexion/extension characteristic shows about 8 degrees lack of extensionin late mid-stance as indicated by the circle 204; and in thevarus/valgus characteristic as indicated at the circle 206, instead of aslight varus signal in mid-stance, we find a 4 degree relative valgus atthis point. These indications are characteristic of a lateral meniscustear.

One set of interrelated features of the present invention deservesrecapitulation. This involves the asymmetric configuration of thegoniometer and its supporting yokes, in combination with thearrangements for mechanically reversing the goniometer relative to thethigh mount and also the electrical circuit reversing arrangements. Moreparticularly, the fact that the upper yoke from which the potentiometersare supported curves to the rear to permit measurement during fullmovement of the leg in all three planes, has previously been pointedout. Also, the corresponding need for reversing the orientation of thegoniometer relative to the thigh mounting cuff has been mentioned, bothwith regard to the three tube embodiment and also relative to the singletube embodiment of the invention. In addition, in connection with thecircuit diagrams, the linked reversing switches for the varus/valgussignal and for the internal/external rotation signal have beenmentioned. The result of these arrangements involves the accommodationof full and and vigorous maneuvers while the plots are being takenthrough the special asymmetric yoke configuration, the use of theidentical unit for both the right and left legs through the mechanicalreversing configuration, and finally, the normalization of the plots forboth the right and the left leg by the use of the electrical reversingswitches for the varus/valgus and for the internal/external rotationsignals. The overall result achieved is a very high sensitivitylightweight unit of universal applicability.

Incidentally, it has been mentioned above that the goniometer assemblyis made of lightweight plastic and is of relatively small configuration.In the description, the slightly larger three-tube unit of FIGS. 1through 5 has been described, and in addition, the one tube unit ofFIGS. 6 and 6A has also been discussed. With regard to their specificconfiguration and constructional features, these two units are both madeof high strength, lightweight plastic, such as Delrin. The rotationalaxes of the two yokes which are included in each of the goniometer unitscross at a single point, and this point is located as close as possiblein alignment with the flexion/extension axis of rotation of the knee. Togiven an indication of the dimensions of the units, the overall heightof the three-tube unit from the upper surface of the upper supportmember 82 (see FIG. 3) to the lower surface of the potentiometer housing46 is approximately 31/4 inches, with the corresponding dimension forthe one tube unit of FIGS. 6 and 6a being approximately 2.9 inches. Inthis regard, the distance from the axis of rotation of the upper yoke toits upper surface for the three tube unit is approximately 2 inches,while the corresponding dimension for the one tube unit is approximately1.5 inches. Similarly, the distance from the centerline of rotation ofthe lower yoke to its lower surface is approximately 17/8 inches for thethree-tube unit and approximately 1.4 inches for the one tube unit.Concerning the spacing of the arms 78-80 making up the yoke for thethree tube unit, the outer dimension is approximately 11/4 inches totalwidth, and the space within the yoke is approximately 1 inch, with theyoke arms 78 and 80 being about 1/8 inch thick; and the outer and innercorresponding dimensions for the one tube unit of FIG. 6 areapproximately 1.115 inches and 0.835 inch, respectively.

Concerning the dimensions of the plastic housing containingpotentiometers 42 and 44, it has dimensions of approximately 1 inch by15/8 inches long by 5/8 inch thick for the three tube unit; and thecorresponding dimensions for the one tube unit were approximately 0.835inch, by 1 inch long by 0.6 inch thick. It is interesting to note thatthe actual size of the goniometer unit including the threepotentiometers is only about 2-3/16 inches in height in the case of thethree tube unit, and only approximately 1.8 inches in height for thesingle tube unit. In addition, the thickness in the direction extendingoutwardly from the knee is only about 11/4 inches across the yoke forthe three tube unit and approximately 1.115 inches for the one tubeunit. From the foregoing dimensions, the very small size of the actualgoniometer unit carrying the three potentiometers is evident, as is thereduced thickness of the unit as aligned with the knee, so that thecenter of rotation may be located very close to the knee.

Incidentally, the potentiometers employed in the three tube unit wereNew England Instrument Company Part No. 55 FL1-120, each having a totalresistance value of 10,000 ohms. The potentiometers used in the singletube unit were plastic film type potentiometers, which were made by theinventors for this particular application.

In conclusion, it is to be understood that the present invention is notlimited to that precisely as described hereinabove. For example, thethree axis goniometer could have minor mechanical and electrical changeswithout departing from the guiding principles indicated in connectionwith the embodiments of FIGS. 1 through 5, and those of FIGS. 6 and 6A;the electrical circuit and the methods described therein could beimplmented by somewhat different arrangements than those specificallyshown and described; and the principles disclosed herein are applicableto goniometer assemblies for measuring joints other than the knee.Accordingly, the present invention is not to be considered limited tothat precisely as described hereinabove.

What is claimed is:
 1. A system for the electrogoniometric study of theknee comprising:a three plane goniometer assembly; means for mountingsaid three plane goniometer assembly adjacent the outside of the knee,said mounting means including means for mounting the upper portion ofsaid assembly from the thigh; said goniometer assembly including a rodof noncircular cross section for rotational actuation by type lower leg;means, including a fitting having an opening for slidably receiving saidrod, for securing to the lower leg; and means for mechanically reversingthe orientation of said mounting means relative to the goniometerassembly by 180 degrees, whereby the identical unit may be used firstmounted on the outside of one leg and then mounted on the outside of theother leg.
 2. A system as defined in claim 1 wherein said goniometerassembly is asymmetric with respect to said mounting means.
 3. A systemas defined in claim 1 including two axis gimbal means for supportingsaid fitting means to transmit rotational movement to said shaft whilepermitting changes in angular orientation.
 4. A system as defined inclaim 1 wherein said goniometer assembly includes a pivotally mountedsubassembly having three potentiometers, and wherein the threepotentiometer subassembly is less than two and one-half inches inextent.
 5. A system as defined in claim 1 wherein said goniometerassembly includes curved open yoke means to preclude interference in themeasurement of the movement of the knee in all three planes despiteconcurrent extreme angular movements of the knee.
 6. A system as definedin claim 5 wherein said yoke includes two legs for pivotally mounting anactive goniometer subassembly, and wherein said legs have an extentalong the pivot axis of less than one and one-half inches.
 7. A systemas defined in claim 1, wherein said goniometer includes threepotentiometers for measuring rotation of the knee in each of threeplanes, and further including recording means for producing graphsrepresenting the rotation of said knee in each of three planes, dataprocessing circuitry for coupling signals from each of saidpotentiometers to said recording means, and means for reversing thepolarity of two of said graphs when said goniometer is shifted from oneleg to the other, whereby the graphs for both legs will be comparable.8. A system as defined in claim 7 wherein said three potentiometersmeasure (1) flexion/extension, (2) varus/valgus, and (3)internal/external rotation, and wherein said polarity reversing meansreverses the polarity of the signals representing varus/valgus, andinternal/external rotation.
 9. A system for the electrogoniometric studyof the knee comprising:a three plane goniometer assembly; means forfixedly mounting said three plane goniometer assembly adjacent theoutside of the knee, said mounting means including a relatively flatmounting plate and means for securing said mounting plate to the outsideof the thigh; said goniometer assembly including means secured to thelower leg for determining internal/external rotation of the lower legrelative to the upper leg; and means for reversing the orientation ofsaid mounting means relative to the goniometer by 180 degrees, wherebythe identical unit may be used first mounted on the outside of one legand then mounted on the outside of the other leg.
 10. A system asdefined in claim 9 wherein said goniometer includes curved open yokemeans with the base of said yoke being mounted to the front and the twoends of said yoke extending to the rear to pivotally connect with theactive components of the goniometer, to preclude mechanical interferencein the course of measurement of the movement of the knee in all threeplanes despite concurrent extreme angular movements of the knee.
 11. Asystems as defined in claim 9 wherein said goniometer includes threepotentiometers for measuring rotation of the knee in each of threeplanes, and further including recording means for producing graphsrepresenting the rotation of said knee in each of three planes, and dataprocessing circuitry for coupling signals from each of saidpotentiometers to said recording means, and means for reversing thepolarity of two of said graphs when said goniometer is shifted from oneleg to the other.
 12. A system for the electrogoniometric study of ajoint between a first and second member of the anatomy comprising:athree plane goniometer assembly; means for mounting said three planegoniometer assembly from said first member adjacent the outside of thejoint; said goniometer assembly including means secured to said secondmember for actuating said goniometer in accordance with the motion ofsaid second member relative to said first member; and means formechanically reversing the orientation of said mounting means relativeto the goniometer assembly by 180 degrees, whereby identical assemblymay be used first mounted adjacent one joint and then mounted adjacentanother similar joint.
 13. A system as defined in claim 12 wherein saidgoniometer assembly is asymmetric with respect to said mounting means.14. A system as defined in claim 12 wherein said means secured to saidsecond member includes a two axis gimbal means and a fitting meansmounted in said gimbal means to transmit rotational movement to a shaftconnected to said goniometer assembly while permitting longitudinalmovement of said shaft PG,24 through said fitting means.
 15. A system asdefined in claim 12 wherein said goniometer assembly includes curvedopen yoke means to preclude interference in the measurement of themovement of the joint in all three planes despite concurrent extremeangular movements of the joint.
 16. A system as defined in claim 12,wherein said goniometer assembly includes three potentiometers formeasuring rotation of the joint in each of three planes, and furtherincluding recording means for producing graphs representing the rotationof said knee in each of three planes, data processing circuitry forcoupling signals from each of said potentiometers to said recordingmeans, and means for reversing the polarity of two of said graphs whensaid goniometer is shifted from one joint to another, whereby the graphsfor the two similar joints will be comparable.